Acoustic Design Mistakes to Avoid

Acoustics should never be a “maybe” on a list of design needs. But what are some common acoustic design mistakes to avoid? We’ve got our best tips right here for you to consider before your next project.

 

One definition of acoustics from the Oxford Dictionary is “the properties or qualities of a room or building that determine how sound is transmitted in it.” Whether sound is ignored or just poorly planned for, a building or room must have appropriate acoustics to be useful.

Now, it’s happened once or twice where someone didn’t think about sound when designing a space, and the results were nothing short of disastrous in terms of acoustics.

london school of economics library

Take, for example, a £30 million library in the United Kingdom. After the London School of Economics library was built by Foster and Partners, the school was flooded with complaints about the acoustics, according to an article published by Architects’ Journal (UK). A spokesman for the London School of Economics reported to the journal that, “’We have been told that even a whisper can be heard anywhere and that the reading areas are far too noisy.” That’s a HUGE problem for a £30 million library! These complaints came about only a few short years after similar issues arose concerning the Faculty of Law building in Cambridge (search on page 83 for details) – a building also designed by Foster and Partners. Exterior noise and reflections were two major issues in the latter case.

Issues such as unintelligible speech, flutter echoes, and too-long reverberation time are just a few other issues that pop up when acoustic design is ignored. What good is a sleek, modern conference room if only 10% of the audience can hear and understand the speaker? Why spend millions designing and building a custom space only to forgo intentional acoustics? Here are a few of the top mistakes to avoid in acoustic design.

1. Ignoring acoustic design

This one seems obvious, yet somehow this mistake in acoustic design happens enough to merit a mention. If an architect or firm has no real knowledge or experience with acoustic design, it is possible to either make recommendations based on guesses or to flat-out provide an incorrect assessment of a space’s design and needs. The two buildings in the United Kingdom by Fosters and Partners are excellent examples of how this mistake can be made in the real world. Therefore, our top tip is simple: don’t ignore acoustic design. It isn’t worth any potential or imagined savings to skimp on getting sound right, so plan on bringing in an expert consultant if this is an area you need help with.

2. Using the wrong materials

Not all materials work for acoustic design, and some don’t work well. While carpet and curtains can curtail some reflections, certain material choices may not be the best option for a space. Finding out and understanding the Noise Reduction Coefficient (NRC) of a product or material, along with knowing the purpose of a room or building, can help determine if it is the right pick. An NRC of 0 means total sound reflection, while an NRC of 1 means total sound absorption. For instance, many throws and smaller carpets have low NRC ratings which may help in sound absorption, but do not contribute a significant amount to overall sound absorption. Only by knowing the use for the room or area can you determine if a felt rug is going to be an appropriate acoustic design.

3. Not sealing all the gaps

Another big mistake when it comes to acoustic design? Doors. Windows. Vents. Electrical outlets. All of these necessary parts of a room or building design must be considered. Sound doesn’t care if the space beneath the main door is only a couple of millimeters — it just wants to keep moving. Like those gappy doors, windows not only allow sound to travel out but also into a space. This can be an important issue, especially in regard to privacy. A leaky door space combined with hard, sound-reflective flooring can take a private conversation to an easily overheard public conversation. Vents and electrical outlets can also allow external noise into a room; it is important to note that certain soundwaves, like bass notes from a guitar, can travel through and be heard more easily than shorter wavelength sounds like singing with certain building materials used in walls.

4. Installing “loud” flooring

Unless you are in a scary movie, you probably don’t need to hear someone else’s footsteps behind you. But that click-clack-click-clack sound is going to get old real fast without considering the Impact Isolation Class of the flooring. One person walking through a long corridor may not be an issue, but multiply that times 12 or 100, and the noise has surpassed most people’s comfort level. The Impact Isolation Class (IIC) measures how well a floor can absorb sound like someone walking. The higher the IIC, the more sound is absorbed. A concrete floor can have an IIC of 25, but most building codes require a minimum of 50 for the IIC rating.  Choose a flooring solution that is going to dampen that sound and keep noise levels to a minimum.

5. Forgetting about the audience

This may seem like it is an easier part of designing a space, but firms like those working in the Cambridge and London examples above neglect the audience. What size does the space need to be? How much natural light is needed? Is the space going to be for musical performance or personal, one-on-one conversations? Will the listeners be young, old, a mix of multiple generations? A library is the exact place where whispering is appropriate and desired, but students could not get the level of quiet privacy they needed because the audience was not considered correctly. Taking in other considerations like hearing maturity and disabilities is also necessary for designing appropriate acoustics.

6. Relying too heavily on technology

Another instance of failed acoustic design comes from Günter Behnisch’s Parliament at Bonn (see page 84) in Germany. In an attempt to make parliament’s meetings “transparent” to all, Behnisch designed a building made of glass walls. These made for a terrible choice for a room that would contain so many officials who needed to speak, be heard clearly, and listen. Because issues of reflection, reverberation, and focus, an extensive sound system was installed by Siemens to give each representative a microphone. Although this was supposed to alleviate any issues or concerns about intelligible speech and clarity, the system did not perform as expected because of a simple human error not discovered until later. Consequently, this led to parliament leaving the building with quite a number of complaints about its design. While the designer had noble intentions, acoustics were clearly not considered or not considered thoroughly enough, rendering the thoughtful architecture virtually unusable until solutions could be implemented. Sometimes, technology can be helpful. However, if a space MUST use an extensive PA system to deliver sound to the occupants, its design should be reconsidered to avoid this mistake in acoustic design.

Although these mistakes in acoustic design could be common sense to those working with sound every day, many firms, designers, and architects just don’t get this part of building a space right from time to time. Make sure to consider these issues before designing to avoid costly mistakes that can ruin a reputation and leave a space empty for lack of appropriate acoustic design.